The Horizontal Loop, also
known as the Loop Skywire Antenna, is an old but very effective design. Although
this design has been around for a long time, it is only gaining popularity now
due to the recent improvement in high power antenna tuners. The main purpose of
constructing this omni directional antenna is to provide a multi band
antenna which performs well from the lowest frequency band for which it is
designed, all the way through 10 meters. It will usually even work well on 6 meters if
your tuner and balun will handle that band. It must be understood that an antenna
tuner (trans match) will be necessary for use as a multi - bander, as well as
the use of twin lead feed line. I recommend 450 ohm ladder (window) line as the feed line.
(See bottom of this page for types of twin lead available). You will of course
need a balun near your tuner, ( I recommend a 4:1 Current Balun ), or a tuner with a
built in Balun, to feed your
rig’s unbalanced antenna connector. I use the
MFJ- 912 (W9INN) Balun. It is a Voltage Balun, but is of good
design, and
works well.

How long to make it. To cut
the antenna wire length to resonance we use the formula:
Length (in feet) = 1005 divided by frequency (in MHz). We must subtract 4% of the total full wave length if we are
using insulated wire. Example : For a 160 meter loop, 1005 divided by 1.800
(lowest 160 meter frequency in MHz) = 558 feet. If using insulated wire, shorten
the overall length by 4% (-22 feet). 558 feet minus 22 feet = 536 feet. This is
due to the slightly decreased velocity factor of insulated wire. The length of
the feed line (450 ohm ladder line) may require some final adjustment or it may
become part of the loop and serve as a radiator. My loop is 520 feet of
insulated wire with a 28 foot lead in, and is resonant slightly below the bottom
of the 160 meter band. I intend to shorten the insulated wire to exactly 508
feet the first time I take it down for any maintenance (Which may be a long
time). You do not need to get it that close to resonance on the lowest band, but
for us anal retentive types it is an interesting distraction. Use this handy Wire Antenna
Calculator(Courtesy of Central California DX Club) for all wire
antennas.

Tuning. This
design is a full wave (or longer) at the lowest frequency for which it is
intended. It need not be cut to resonant length even for the lowest frequency
band intended. It can be cut longer, even much longer, letting your tuner handle
the mismatch. The most practical design however is to cut it to resonance at the
lowest frequency of the lowest band targeted as outlined above. With some
adjustment of the length of the feed line, you may find several bands or
portions thereof which will be resonant enough to allow you to bypass the
tuner. If using a separate balun to
feed your tuner, try to keep the connecting coax as short as possible. 10 to 15
feet or less should not be a problem.

How High.
Ideally, this antenna should be hung as high as possible, but even at very low
height (as low as 10 to 20 feet above the ground) it can be very effective. Be
sure to hang it high enough that it cannot be contacted by anyone on the ground.
It can be hung beneath the canopy of the trees as long as the wire does not
touch any leaves, branches etc. Note: If insulated wire is used, contact with
leaves or branches is permissible, but is best avoided to prevent the insulation
from eventually being damaged.

What if I don't have
room for a 160 meter loop ? Make the loop as large as
your property will allow. If you can cut it for 160 meters go for it. If
not, go for 80 meters or 40 meters. A 40 meter loop requires less than 130
linear feet of insulated wire. That is a square of only 33 feet per side. Nearly
any suburban residential lot should be able to accommodate that size. Remember
the sides need not all be equal, it can be almost any shape that encloses the
largest area possible. EXPERIMENT !

At first blush, this design
may appear to be just a big short circuit because each leg of the feed line is
connected to the end of a big loop of wire. True, it is a short circuit at D.C.
but at Radio Frequency, which is A.C., it is an excellent radiator. Do not be
misled by reports (mostly from those who have never tried it) that this is only a
vertical radiator or “cloud warmer” design. When used with ladder line you will
be impressed with its performance as a transmitter antenna and surprised at how
quiet it is as a receiving antenna. Naturally though, performance will increase
somewhat with height above ground.

I strongly suggest the use of 12
gauge stranded, insulated, copper wire, which can be purchased at Home Depot and
other home improvement centers for about $ 40 for a 520 foot roll. That is enough to make a 160 meter loop. The loop should be hung as high as is
practical, and should be in the approximate shape of a big circle or square. It
need not be perfectly horizontal, and the shape can really be a big square, or
rectangle or any multi sided shape, so long as the two ends meet at convenient
point where an insulator can be used to attach the feed line. The most
critical element is that the loop should encircle the largest AREA possible. A
circle, or square, or rectangle, is much better than an elongated oval, or triangle, or dog bone
shape. My 160 meter loop is 7 sided, with none of the legs of equal length or
height, and it is a stellar performer. It is 25 feet above ground at the highest
point, and 15 feet at the lowest. Mine is 520 feet in total length.

The loop can be attached to
poles, trees, buildings etc., whatever is convenient. It is best of course to
try to avoid running it with a leg parallel to nearby power lines. NEVER
INSTALL ANY PORTION OF THE LOOP OR FEEDER LINE ABOVE OR BELOW A POWER LINE!
The loop can be free floating (that is attached so that it can be pulled tight
at the two ends and just looped through the guy lines that hold it up) or it can
be firmly attached at one or more points as necessary. I use heavy (5/16 in.) black
Dacron rope with a knot that is loosely tied to the wire. Mine is free floating
so that if I disconnect the center insulator, the entire loop will go slack, but
will still be loosely attached to the guy ropes. This is probably the best way to
hang
it, especially if it is attached to trees, as it allows for some movement as the
trees sway, and does not stress the wire. If it is left free floating or
partially so, it is a good idea to leave a little slack in the wire. There is
no reason to stretch the wire guitar string taut. Unless you are using a high
power amplifier in a very wet environment, it is not really necessary to use
insulators to attach the Dacron guy ropes to the wire when using insulated wire,
as the Dacron rope does not tend to absorb much moisture. I highly recommend the
use of Dacron rope due to its strength and resistance to deterioration from
sunlight and the weather. This rope can be purchased from most ham radio stores
and is available from MFJ, HRO, DX Engineering and AES. Note: This
may be called Dacron, Dacron/polyester or
Dacron/nylon rope, or just polyester antenna rope, and should not be confused with Dacron wire rope, which
has wire woven into it, and is sometimes used as an antenna wire. It is unlikely that you will find
Dacron rope at a
local hardware or home improvement store. Whatever type insulator you choose as
the attachment of the two ends of the wire to the lead in, be sure to solder
the antenna to the lead in wires well. I use a piece of PVC pipe as the insulator. The antenna can be fed
at ANY point. I chose to feed it near the end of one leg for convenience. The
feed line should be at an angle to the antenna wire, a 90 degree angle if
possible to prevent coupling of the feed line to the antenna wire.

I want to stress the
importance of several points:

Remember, each end of the
wire loop attaches to one of the legs of the lead in wire.

The higher above ground you
can hang your antenna the better.

Enclose the largest area
possible. This is the key to great performance.

For best long term results,
I recommend the use of #12 insulated stranded copper wire. The best color
is black, as it is sunlight resistant and less visible. This wire is also quite
strong and flexible, and the insulation reduces precipitation static.

Use black Dacron rope (Not
Dacron wire rope), to tie
it up. Just about any other rope will rot away in a year or so. NEVER use metal wire or wire
rope as it will interact with the antenna and screw things up royally. If you
choose not to use Dacron rope, I suggest using heavy, non - metallic Trot Line Cord which can be
found at sporting goods stores, or in catalogs catering to cat fishing enthusiasts.
It is strong and rot resistant but will not last nearly as long as Dacron rope.

For best results, I recommend that you do not try to use it at a
frequency lower than the lowest resonant frequency. (Don’t try to load an
80 meter loop on 160 meters) It will perform well at higher frequencies with a
tuner. If you experiment with loading it on a lower than resonant
frequency, try it at very low power while attempting to adjust your tuner for
minimum SWR.

Do not feed It with
coax unless you install an automatic, remote tuner at the antenna feedpoint.
(Note: See Alternatives to Twin Lead section
below). This is a MULTI band antenna, and 450 ohm ladder line will have very
little loss at non resonant frequencies. Ladder line is not that difficult
to deal with. You can cut a slit in your attic etc. to feed the line in. Just
keep it 3 or 4 inches from any metal and don't bend it in a radius tighter than
10 or 12 inches. You can run it to a 4:1 Balun under your eaves for example, and
then run a short length of coax into your shack. Experiment a bit and see what
works best for you. 600 ohm open wire line will also work well, but is not as
readily available, nor as easy to work with as the insulated 450 ohm window
line.

If you have trouble getting
it to tune to minimum SWR on any band or experience RF in the shack, try
lengthening or shortening your ladder lead in line. In a worst case scenario, it
may be necessary to change the position of the feed point.
Some bands may exhibit lowest SWR when the tuner is bypassed. Experiment as necessary.
If using a manual tuner, draw up table of the necessary tuner settings at
various frequencies, for quick reference when tuning.

A word of caution:
These big loop antennas are a large target for a lightning strike, either a
direct or nearby hit. They can also build up a significant static charge from
precipitation or dust in the atmosphere. It is crucial to disconnect the lead
in, and ground it ( direct to ground outside the shack ) if possible, before an electrical storm approaches. To
prevent equipment damage from static charge buildup, always ground both leads of
the window line, (or center wire and braid if using a coax run to your tuner)
momentarily, before connecting the feed line to your tuner or an antenna
analyzer.

Here is a link to an
outstanding article regarding the use of ladder line: Check it out.-----

Types Of Twin Lead

300 Ohm Twin Lead

450 Ohm Window Line

True Ladder Line - Normally 600 Ohm

Also Called TV Lead In

Also Called Ladder Line

Also Called Open Wire Line

Alternatives to Twin
Lead

For those reluctant to use twin
lead, there are several new alternatives, which allow the use
of coax feedline, with minimal losses, even on non resonant frequencies.

MFJ has recently introduced two new remote high power tuners. These are the MFJ-998RT, rated at
1,500 watts SSB & CW, and the similar MFJ-994BRT, rated at 600 watts. Click
below to view them in the latest MFJ Catalog. These tuners are claimed to be
completely weather sealed, and are powered through the coax feedline via an
included power injector. Both units are designed for use from 160 through 10
meters.

These are relatively new products,
but I have had good reports on them.

LDG Electronics also makes a
couple remote tuners, the
RT-100 tuner that can handle 100 watts, and the
RT-600, capable of handling 600 watts. I understand they may soon be
adding a higher power version to their line up. These are brand new
products, and I have not yet seen any reviews of them. If anyone tries them out,
please e-mail me and let me know how they perform.

Frequently Asked Questions

Q.
Why do you recommend a 4:1 balun when using 450 ohm or 600 ohm feed line?

A.
The 4:1 balun is readily available, and offers the best overall compromise for a
multiple band loop antenna. It will normally provide an impedance which your tuner
can work with at all frequencies for which your antenna is designed. Remember
that the impedance listed for feed line in only its characteristic
impedance. The actual impedance varies with the frequency of the signal. A 1:1
balun will probably work with most antenna systems.

Q.
Which is best, a voltage balun or current
balun ?

A.
A current balun has some advantages
regarding efficiency and core saturation issues. A good voltage balun,
rated for the power you intend to run will work quite well in most
circumstances. I recommend using a voltage balun if you already have one. If you
are buying a new one, a current balun will be a slightly better choice in the
long run.

Q. Why do
you recommend the 450 ohm window line instead of open wire or 300 ohm TV twin
lead ?

A.
Even though it has slightly more loss, the ladder line is easier to work with,
and more readily available than true open wire line. The TV twin lead has too
much loss, and will not handle very much power.

Q.
How long should my twin lead feed line be ?

A.
Long enough to reach your tuner or balun, plus a few additional feet for
trimming.Good lengths (in feet): Somewhere around 40,
80, 110, etc. Lengths to avoid (in feet): 32, 65, 96, 130, and 260 - and
multiples of any of those. If in doubt, consult the ARRL Antenna Book.
Having said that, I recommend that you simply make it a bit longer than
necessary, as previously stated. Then, if it won't tune on a certain part of a
band or bands, or if you experience RF in the shack, shorten
the feed line a foot or so at a time until you hit the sweet spot and overcome
the problem. An antenna analyzer will be of great value here. Although it is
easier to cut the line to shorten it, all twin lead can be lengthened by
splicing. Just do a good soldering job, and seal the splice with epoxy or liquid
electrical tape. If using coax as your feed line, don't worry about the
length. Just use a long enough run to reach your shack.

Q. What
should I do with the extra length of twin lead if I hit the sweet spot and don't
want to shorten it ?

A.
Run it back and forth in a zig-zag pattern, or in large loose coils away from
any conducting material. Do not coil or roll it back up on itself.

Q. Can I make an attic loop
antenna, or a loop around the perimeter of my roof ?

A. You sure can, and in this era of CC&R antenna
restrictions, it may be your only choice. Of course it will not work as well as
one up clear and high in the air, but you will probably be surprised at how well
it works. It will be better than almost any other stealth type antenna, if you
have room for it. Try to keep the antenna wire a few inches off the roof by
short PVC or wooden standoffs, or hang it under the eaves. Naturally, as with
any other near house antenna, you may experience some RFI issues both to and
from household wiring and appliances, but IF you have such problems, they can
normally be cured by the judicious use of chokes and toroids. The ARRL RFI
Book is an excellent reference on how to avoid and cure such potential
problems.

Q.
Can you help me understand why twin lead is a much better choice than coax for
feed line on multi band or other non resonant antennas ? Doesn't the tuner
transform the impedance to 50 ohms and bring the SWR down just as well with coax
?

A.
When you are using coaxial cable under high (greater than
3:1) SWR conditions, the tuner may provide the 50 ohm match to your radio,
but the mismatch and HIGH SWR still exists between the antenna tuner and the
antenna! This translates to very high losses in the coaxial cable. At
HF frequencies, the loss in ladder line is so low, you can still see good
results even when
the SWR between your tuner and antenna feed point is horrendous. The antenna tuner provides the 50 ohm
match to your radio, and you really don’t care what the SWR is between the tuner
and the antenna, due to the inherent low loss of twin lead. Use this handy
On - Line Calculator to determine coax loss. On - Line Coax
Cable Loss / Antenna Gain Calculator

Q. Will the built
in auto tuner in my transceiver be sufficient for use on a multi band loop
antenna ?

A. Unfortunately
it probably will not. Those tuners are only capable of handling a mismatch of about 3:1
or so. You will be encountering much higher ratios than that, hence the need for
a good stand alone tuner. Most manual and automatic tuners on the market today
will do a good job, as long as they are capable of handling the power levels you
will be running (in the future as well as when starting out).

Q. I
already have a horizontal loop fed with coax. I am able to obtain a low SWR
reading on all the bands at and above the fundamental frequency, using my stand
alone tuner, but the antenna does not seem to perform well on several bands. How
can I determine which bands will most improve by changing to twin lead ?

A. With your
tuner bypassed, use either an antenna analyzer, or your radio’s SWR
meter, and measure the SWR at various points throughout the 80 to 10 meter
bands. Those frequencies where you have SWR of about 3:1 or higher are the spots
where you will most benefit from the use of twin lead.

Bear in
mind that when your tuner is used, SWR indications can be adjusted to near 1:1
on most bands, even using coax as your lead in. That is because you are only
measuring the SWR between tuner and radio. That will keep your modern solid
state radio happy seeing about 50 ohms, so it will produce full power without
folding back power to protect your finals. However, when using coax on the non
resonant frequencies, most of that power is not radiated, since it is simply
wasted heating up your coax.

When you
change to using twin lead, most of that same power will not be wasted, but will radiate
from your antenna due to the inherently low loss of twin lead, even at non
resonant frequencies. The Standing Wave will still actually be present on your
twin lead, but it does not matter since it will make it to your antenna where it
will radiate. You won’t see the difference on your power meter or SWR meter,
but you will be putting out a much stronger signal, and should get good signal
reports. You will also notice a marked improvement on received signals.

As a
reminder, if you have trouble getting good SWR readings on some frequencies,
experiment by slightly changing the length of your twin lead, or in severe cases
even relocating the feed point.

Q. How
much power do I actually lose with coax VS twin lead ?

A. Assume that you have a 100-W transceiver
connected to one of the transmission lines listed below. How much power (in
watts)

actually makes it to your antenna ? Examples are shown for 80,
10 and 2 meters, with 100 feet of transmission line and SWRs of 1:1

and 6:1 on each of these bands. Remember that SWR can easily
exceed 10:1, and is often even much higher, on a non resonant (multi band)
antenna.

TABLE: SWR Power Loss For Various Types Of Transmission
Cables Note: These losses are in DECIBELS, not percentage of
power.

It’s worth noting that ladder line exhibits substantially less
loss on the HF bands than just about any other transmission line available. This
means you can get away with SWRs on ladder line that would cause intolerable
loss with coax.

The object of any antenna system is to get RF into the antenna,
and out on the air. Your transmission line plays a critical role in getting this
job done. When you shortchange yourself on transmission line, you shortchange
your whole station. As long as an antenna tuner is used, ladder line offers some
compelling advantages compared with coaxial cable in almost any medium- or
high-frequency application. This is particularly true when you want multiband
operation with a single antenna.

Q. Is the increased performance of a twin lead
fed, multi band antenna really worth the effort VS coax fed ?

A. See the excerpt below, from
"Understanding SWR By Example" by Darrin Walraven, as published in the November
2006 issue of QST Magazine, and judge for yourself.

READ & UNDERSTAND THIS

-----

Good luck with your project.
Chances are you will be so pleased with this antenna that you will no longer use
any other wire antenna at or above the resonant range of your Horizontal Loop. Please
let me know how it works for YOU.

If I can be of any
assistance, please e-mail me at
k5rcd@wildblue.net but first, please read the Frequently Asked Questions
section above.

-----

Recommended Reading

Some links to articles and information that
will provide valuable insight regarding antenna systems: